CRUSTACEA MALACOSTRACA. IV. 



what smaller family Leuconida;, of which not a single species is tropical, has a very high number of species, 

 viz. 22, in our area. 



As to number of species in our area a comparison of the Cumacea with Isopoda and Tanaidacea 

 is rather suggestive. Of the order Tanaidacea Sars described 28 species from Norway, while I (1913) enumer- 

 ated from the "Ingolf" area 78 species, 52 of which were new to science; of Isopoda Sars has 84 species from 

 Norway, while I (1916) counted from our area 164 species, 70 of which were new. Compared with these 

 astonishing results the outcome as to Cumacea is proportionately moderate, viz. from Norway according 

 to Sars 49 species, while I enumerate 66 species, 24 among them new. As a very large number of the Tanai- 

 dacea and many Isopoda are smaller and not more easy to detect in sifted bottom material than the Cumacea, 

 and as the animals of all three orders have been searched after with the same care and interest in the same 

 samples, it follows that the fauna in our area of the last-named order must be much less exceeding that of 

 Norway (or Great Britain) than is the case with that of Tanaidacea and Isopoda in proportion to the Nor- 

 wegian (or British) fauna of these orders. An explanation can partly be derived from some facts to be pointed 

 out later on as to bathymetrical distribution. 



B. The Classification. 



The shape and morphological structure of the appendages is on the whole well known at least in one 

 form and frequently in some species of most genera. Nevertheless, the value of a number of genera is rather 

 questionable, and, what is more important, some of the families are not very well defined. G. O. Sars, the 

 first author who divided the order into families, accepted in 1879 8, in 1899-1900 9 families ; Caiman established 

 a new family on an aberrant form discovered at Ireland, but both the last-named author and C. Zimmer 

 pointed out in various papers the difficulty or impossibility of maintaining a few of the older families, and 

 the result is that 3 were cancelled, so that Zimmer in 1913 has 7 families; this arrangement is, I think, the 

 best hitherto proposed. Stebbing divided in 1912 and in "Das Tierreich", 1913, the order into 26 families, 

 but this radical splitting has already been criticized by Zimmer, and I cannot follow the highly meritorious 

 English author in his classification. But his attempt has a peculiar interest, because it is a symptom or indi- 

 rect indication of the difficulty every Zoologist will find in trying to circumscribe natural and well defined 

 families in this order. In my opinion we must know at least twice, perhaps three times as many species as 

 hitherto described — especially of the fauna living in from 100 to about 600 fathoms in tropical and sub- 

 tropical seas — before we can hope to ameliorate the classification in points essential. And perhaps the task 

 will prove itself partly insoluble, as seems to be the case in the suborder Amphipoda Gammarida. 



In the present paper not the slightest attempt of reform as to families has been made. The large ma- 

 terial contained certainly a good number of new species, but not one among them differed so much from a 

 previously well-known species, that it became necessary or even possible to establish a new genus tor its 

 reception. And the types of the genera dealt with here were all well studied. The only thing I could make is 

 in a few cases to lay more stress than generally made on some differences serviceable as specific characters ; 

 for inst. the shape, relative size and serration of the joints in third pair of maxillipeds in Procamfylas/ns : and 

 Camfiylaspis (and perhaps in several other genera) ought to be considered more carefully than generally believed. 



